The ultraviolet-irradiated hairless mouse: a model for photoaging.

The hairless mouse is proving to be a relevant model for the systematic study of photoaging. As in humans, with chronic ultraviolet radiation, these mice develop elastic fiber hyperplasia, followed by elastosis and ultrastructural degradation. Collagen is damaged and its metabolism is altered, while the normally low levels of proteoglycans and glycosaminoglycans are greatly increased. With this model we have described the effects on dermal connective tissue of UVB (290 to 320 nm), UVA (320 to 400 nm), and the combination of the two. We have also assessed the protective effects of sunscreens. We found that a significant amount of photodamage was repaired when ultraviolet radiation was stopped. Subepidermally in a former region of elastosis, a band of new normal dermis was laid down. Enhancement of the repair was achieved with topical all-trans-retinoic acid in a time- and dose-dependent manner. Retinoic acid was also found to induce angiogenesis in unirradiated mice.